Today's tasks of providing medium to high security control of access to a resource (such as entry to a facility or use of a service) increasingly employs biometric authentication of enrolled users. Authentication includes the cases of (1) verification, in which the user claims a specific identity and (2) identification, in which the user does not assert an identity, and where the system must hypothesize the user identity. Verification tasks typically have lower computational requirements and higher confidence due to their lower perplexity relative to the identification tasks.
Biometric authentication may be made more secure by challenge/response protocols. For example challenge/response protocols thwart replay attacks in which the bio-signature of the enrolled user is recorded and replayed to the system in a subsequent attempt to gain access. In challenge/response protocols the response required of the user depends on the challenge provided by the system. Text-independent speaker authentication biometrics are particularly well suited to challenge/response protocols, as unlimited variation of the speech responses may be made to the text-independent speaker verification system.
Typical user authentication systems prompt the user with one or more questions, each having a unique answer. For example: “Please say your password” or “what is your mother's maiden name”. These answers may readily be compromised, when other persons may listen to or otherwise observe the session, especially in the case of speaker authentication. Thus, the need remains for a challenge/response user authentication system and method that more adequately thwarts an interloper seeking to anticipate appropriate responses. The present invention fulfills this need.